The invention relates to a hand tool machine, in particular to a drilling machine.
In European patent application No. 0,018,465, the hand tool machine is provided with a feeler device for determining the diameter of tool elements used in the hand tool. The position of the chuck jaw of a drilling chuck is determined by a feeler to provide a value which is transmitted to a control unit for the motor of the hand tool machine. The rotational speed of this motor is controlled corresponding to the indirectly determined shank diameter of the tool element inserted into the chuck.
This principle seems to be rather sound. However, it possesses some disadvantages which reside primarily in the determination of the diameter by analyzing the position of the chuck jaw. Since it frequently happens that the drill shanks are stepped and the drill bits have cutting edges projecting radially beyond the diameter of the actual drill body (hard metal drill), the determined shank diameter does not correspond to the working diameter of the drill bit. Consequently, wrong settings are unavoidable. Moreover, the hand, tool machine according to European patent application 0,018,465 provided with such a control device does not provide the operator with information about the diameter of the inserted drill bit.